Few people seem to have noticed that the law of murder in England and Wales changes on Monday. With only a few days to go, the Ministry of Justice had not published the circular it normally issues in good time to inform "public and stakeholders" – in this case, killers and courts – about changes in legislation and their commencement dates.

The main change to the law of homicide deals with provocation. At the moment, people who kill after being provoked into losing their self-control may have a defence to murder. But it's not a full defence, which would result in an acquittal. Provocation is a partial defence, meaning that it leads to a conviction for manslaughter rather than murder.

This is crucial – but only because murder attracts an automatic sentence of life imprisonment, while the sentence for manslaughter is within the court's discretion.

Men who kill out of anger can plead that they were provoked to lose their self-control by something done or said by the victim … Women who kill …out of fear of violence cannot easily fit into the same defence. Typically, they strike out with a knife in fear as their partners approach to inflict another beating.

So women are convicted of murder while men get away with manslaughter.

Before the general election, Labour took the necessary steps to change the law from 4 October. The reforms apply to killings on or after that date.

• the killing resulted from a loss of self-control; • the loss of self-control had a "qualifying trigger"; and • a person in the same position "with a normal degree of tolerance and self-restraint" might have reacted in a similar way.

A qualifying trigger can be: a fear of serious violence; or something said or done that was "extremely grave" and gave the defendant "a justifiable sense of being seriously wronged"; or both.

In deciding whether the loss of self-control had a qualifying trigger, the courts must ignore such factors as sexual infidelity and a desire for revenge.

If all the above makes your head spin, bear in mind that I have done my best to simplify the law by leaving out many of the details. Although the new law will make it easier for some defendants to establish manslaughter, it will be harder for others to escape a murder conviction.

The victim's sexual infidelity will no longer be grounds for reducing murder to manslaughter and a defendant who kills in anger will be able to rely on the defence only in extremely grave circumstances. On the other hand, a person who kills in response to a fear of serious violence should be able to put forward the defence on that basis rather than trying to shoe-horn it into a defence based on killings in anger.

On the whole, this strikes me as a sensible rebalancing of the law. The coalition was right not to block its implementation. However, there is a much simpler solution to the problem.

It is obviously right for society to treat some killings more seriously than others. But the dividing line between murder and manslaughter would matter much less if we changed the law on sentencing. Life imprisonment should be the maximum sentence for murder, not the mandatory sentence.